The overall goal of this project is to assess whether exposure to endocrine disrupting compounds during pregnancy is associated with a) adverse development (cognitive function, height, weight, weight for height, and for females, age at menarche) in the offspring at birth, early childhood, middle childhood, and adolescence, b) mild deficiencies in maternal thyroid function, and c) whether adverse developmental findings, if any, are attributed in part to deficiencies in exposure to maternal thyroid hormone in utero. The proposed study draws on data from the Child Health and Development Study, a longitudinal follow up of children born between 1959 and 1966 to mothers enrolled in the Oakland, California membership of the Kaiser Foundation Health Plan. Prenatal sera has been appropriately frozen and stored, and are available to assess both exposure to organochlorine compounds and maternal thyroid function during pregnancy. Serial measures of growth are available in the same children from birth to age 17 years, as are standardized developmental examinations at ages 5, 9-11, and 15-17. The proposed measures of organochlorine exposure and exposure to measures of maternal thyroid function (thyroid stimulating hormone, free thyroxine, thyroid peroxidase antibodies and transthyretin - a protein responsible for the transport of thyroid hormone). Statistical analyses will estimate associations taking advantage of the repeated measures structure of the data. The analyses will employ generalized estimating equations (GEE) methods for repeated measures, taking account of potentially confounding variables. We will distinguish effects of prenatal organochlorine exposures from infancy through adolescence. We will also investigate a specific mechanism: via maternal thyroid function. Results will fully describe the effects of prenatal exposure and will also further knowledge about the relation between subclinical maternal thyroid hormone deficiency and childhood development. This line of research could lead to prenatal interventions.